The invention relates generally to the manufacture of electronic devices. More specifically, this invention relates to pattern-formation methods useful in the formation of fine lithographic patterns.
In the semiconductor manufacturing industry, photoresist materials are used for transferring an image to one or more underlying layers, such as metal, semiconductor and dielectric layers, disposed on a semiconductor substrate, as well as to the substrate itself. To increase the integration density of semiconductor devices and allow for the formation of structures having dimensions in the nanometer range, photoresists and photolithography processing tools having high-resolution capabilities have been and continue to be developed.
Positive-tone chemically amplified photoresists are conventionally used for high-resolution processing. Such resists typically employ a resin having acid-labile leaving groups and a photoacid generator. Patternwise exposure to activating radiation through a photomask causes the acid generator to form an acid which, during post-exposure baking, causes cleavage of the acid-labile groups in exposed regions of the resin. This creates a difference in solubility characteristics between exposed and unexposed regions of the resist in an aqueous alkaline developer solution. For a positive tone photoresist, exposed regions of the resist are soluble in the aqueous alkaline developer and are removed from the substrate surface, whereas unexposed regions, which are insoluble in the developer, remain after development to form a positive image.
Lithographic scaling has conventionally been achieved by increasing the numerical aperture of the optical exposure equipment and using shorter exposure wavelengths. At present, ArF (193 nm) lithography is the standard for mass production of advanced semiconductor devices. To form finer device geometries than possible with ArF lithography, EUV lithography methods and materials have been and continue to be developed for next-generation devices. A technique to reduce pattern geometry beyond that attainable by direct imaging alone is photoresist pattern trimming (see, e.g., US2014/0186772A1 to Pohlers et al). Pattern trimming processes typically involve contacting a photoresist pattern that includes a polymer having acid labile groups with a composition containing an acid or thermal acid generator. The acid or generated acid causes deprotection reaction in a surface region of the resist pattern, which region is then removed, for example, by contact with a developer solution. The features of the resulting resist pattern are thereby reduced in size as compared with the original resist pattern.
With the reduction in pattern size and resulting device geometries, linewidth roughness (LWR) of the photoresist pattern is becoming an increasingly important source of error in lithographic processing (see, Mack, Understanding the efficacy of linewidth roughness postprocessing, J. Micro/Nanolith. MEMS MOEMS, 033503-1 July-September 2015, Vol. 14(3)). As such, it would be desirable to minimize LWR of the formed resist pattern.
There is a need in the art for pattern-formation methods useful in electronic device fabrication that address one or more problems associated with the state of the art.